HOUSTON  Considering all the circumstances — not the least of which was the intensity of his triple-digit velocity — the out-loud wonder was whether Padres right-hander Andrew Cashner could even last 90 pitches Thursday night.

He did.

Indeed, on the 91st pitch, Cashner finally gave up his first hit. On a 99-mph fastball. In the seventh inning.

Almost as if determined to make sure Cashner got a win that seemed to have slipped away from him, too, the Padres scored an almost unfathomable six runs in the top of the ninth for a 7-3 triumph and series split with the Houston Astros. Thrown out at the plate on what might have been the tying run in the ninth inning of a loss the night before, Alexi Amarista delivered the series-finale win in highly unlikely fashion, smacking a two-out grand slam off closer Brett Myers.

“My first (major league) home run,” said Amarista. “My emotions got to me.”

One hundred and 19 straight times, the Padres had failed to win a game they trailed after eight innings, and this one sure didn’t look like it’d be anything but No. 120. But then, Houston helped, third baseman Chris Johnson perpetuating the late rally with an error and Myers tying the game at 3-3 by plunking Carlos Quentin with the bases loaded.

“The thing about Alexi ... we use the term “hitterish,’ ” said manager Bud Black. “Even though he’s slight of stature (5-foot-6, if that), I mean, he takes a rip ... Hey, he’s always ready to hit. His intent is to hit, not to take pitches. Today, he hit.”

“I was just looking for a good pitch,” said Amarista. “I got it.”

Although unsure that he’d gotten all of it until the ball cleared the right-field wall, Amarista said he knew right away that the ball was not going to be caught, and so did a Padres bench that went fairly berserk. Among them was Cashner.

“That’s a big rip for us right there,” said Cashner, who stands at least a foot taller than Amarista. “He’s got a lot of fight in him. For him to come up big in that situation, that was huge for us as a team.”

Until that ninth, the Padres’ story had been all about Cashner, and not just because he went so long into the game before that first hit.

“He’s eight outs from a no-hitter,” said Black, “but a true professional got a base hit.”

Carlos Lee’s clean, line-drive single landed in the grass in left-center, wrecking what would have been a no-no for the only major league franchise that’s never had one. And on the 10st pitch, Cashner gave up a two-run homer to Brian Bogusevic, erasing the 1-0 lead Cashner had protected so fiercely.

Exactly as left-handed starter Clayton Richard had done the night before, then, Cashner left the game with a two-hitter and a one-run deficit. Relief pitcher Nick Vincent gave up the third Houston run on a walk, hit and wild pitch, but wound up with his first major league win.

For the longest time, Cashner had put a serious buzz in what’s already been a long and impossibly difficult season for the Padres, even if baseball is yet to reach its All-Star break. Perhaps most remarkable was the fact that it came in Cashner’s first real start for the Padres, who had him begin the season in the bullpen after dealing for him in the offseason.

Coming off three starts at San Antonio that were purely intended to build up his stamina, work on his breaking ball and focus more on deterrents to the running game — but also jazzed to be pitching just an hour from his home in Montgomery, Texas — Cashner got the first of his nine strikeouts by smoking Lee with a 100-mph fastball.

Striking out the side in the third — all swinging — Cashner dialed it all the way back to 98 and 99 mph. In the fifth, he threw an 88 mph change-up.

It didn’t hurt that Cashner was working with a lead. Chase Headley had taken care of that with a solo homer into the Crawford Boxes in left, the third baseman’s eighth home of the season, double his 2011 total.

“This is a big momentum shift for us,” said Cashner as the Padres prepared to head to Colorado for three games. “A lot of guys got to stand back and take a deep breath.”